Thermionic valves



Nov. 22, 1960 v. s. BAWDEKAR 2,961,567

THERMIONIC VALVES Filed March 25, 1959 VAMAN SHANTARAT-T BAY'IDEKAR BYZip- '11 INVENTOR United States Patent THERMIONIC VALVES Vaman ShantaramBawdekar, London, England, assignor to Siemens Edison Swan Limited,London, England, a British company Filed Mar. 23, 1959, Ser. No. 801,265

Claims priority, applicationGreat Britain Apr. 10, 1958 2 Claims. (Cl.313-270) This invention relates to thermionic valves and particularlyconcerned with the maintenance of the spacing between a tubular cathodeand a surrounding anode whilst at the same time preserving a high degreeof insulation between them.

It is the usual practice, in thermionic valves of the kind having atubular cathode and a surrounding anode of tubular form coaxialtherewith, to maintain the cathode concentrically within the anode bymeans of mica spacers located at opposite ends of the anode, the micaspacers having apertures through which the ends of the tubular cathodeproject. It is necessary to fasten the cathode to the spacer at the endof the anode remote from the base of the valve so as to prevent relativemovement axially of the cathode between the cathode and the spacer.

In some valves where a high degree of cathode-anode insulation isrequired, such as booster diodes, it is essential that any metallicmeans used to fasten the spacer to the cathode should not reducecathode-anode clearance and degrade the insulation between theseelectrodes.

The object of the invention is to provide a method of securing thecathode tube to the mica spacer in a manner which will avoid anyreduction in the insulation between the anode and the cathode.

In a thermionic valve having a tubular cathode and an anode surroundingthe cathode, the cathode being held within the anode by means of atleast one mica spacer which engages the anode and is apertured toreceive the cathode, according to the invention, the cathode is providedwith a projection which locates it against the spacer, and the spacer isheld towards the projection from the cathode by means of a metal membersecured to the cathode tube at a region spaced along the tube from theprojection, the metal member extending towards the projection andabutting directly or indirectly against the face of the mica spacerremote from that which engages the projection. The metal member mayextend along the surface of the cathode tube to which it is secured soas to engage the mica spacer in the immediate vicinity of the cathodetube; alternatively, it may be arranged to extend from the cathode tubeto engage an insulating member preferably of ceramic material which ispositioned within an aperture in the mica spacer displaced from thatthrough which the cathode tube extends, and rests on a section of theanode or any other convenient part of the electrode structure.

In a preferred construction a combination of these two features isemployed the metal member being secured to the cathode intermediate itsends, one end of the metal member beyond the region at which it issecured to the cathode tube extending towards the mica spacer to retainit against the projection on the cathode tube, whilst the other end ofthe metal member is utilised to form the conductive connection to thecathode and is supported against movement by engagement with aninsulating member engaging an aperture in the mica spacer and resting ona section of the anode or any other convenient part of the electrodestructure.

ICE

The improved effect by these alternative constructions resides in thefact that the wire or strip does not extend along and in contact withthe surfaces of the mica and does not therefore reduce the insulationvalue of the mica spacer between the cathode and the anode.

The invention will now be described with the aid of the accompanyingdrawing, in which Fig. 1 is a perspective view of one end of a cathodeanode assembly suitable for use in a booster diode,

Fig. 2 is a cross-section of part of the electrode system to an enlargedscale to show the construction of the retaining means for the micaspacer, and

Fig. 3 is a view similar to Fig. 2 of an alternative arrangement.

Referring to Fig. 1, we have illustrated the upper end of the electrodesystem of a booster diode showing the tubular cathode 1, located withina surrounding tubular anode 2, the relative positions, of the anode andcathode being maintained by-means of a mica spacer 3; Spacer 3 is shownas being arranged to engage at-its periphery the inner wall of theenvelope 4, the mica spacer being formed with angularly displacedprojections 5 which bear against the inner wall of the envelope 4. Thetubular cathode is provided with a heater 6. The cathode tube 1 iscoated with a suitable electron-emissive material on that part of itwhich extends through the anode 2.

Anode 2 is provided with radially extending fins 8, of which four areshown, the fins serving both to assist thermal radiation from the anodeand to locate the spacer 3 through apertures in which the upper ends ofthe fins 8 project. A similar spacer will be provided on the lower endof the anode, not shown, and retained in position in any suitablemanner.

Cathode 1 extends through a central aperture in the spacer, and thespacer is located by providing it with an annular projection 9 shown inFig. 2. In order to retain the projection 9 against the mica spacer 3,according to the invention, a wire 10 is secured to the cathode tube at11, e.g. by welding, at a region spaced along the tube from theprojection 9, the end of the wire 10 extending towards the projection 9and abutting directly against the face of the mica spacer 3 remote fromthat which engages the projection 9. The end of the wire 10 thus engagesthe mica in the vicinity of the cathode and does not extend along thesurface of the mica to reduce the insulation value thereof. Beyond thepoint of connection 11 to the cathode tube 1, wire 10 extendssubstantially parallel to the surface of the mica and is then bentupwardly to engage with connection 12 which is sealed through the wallof the envelope 4 to make contact with an external metal cap 13 whichconstitutes the cathode terminal.

In order to relieve the connection 11 from stress during the manufactureof the valve, wire 10 is supported by a wire 14 which is welded to thewire 10 and the end of which is inserted into an insulator 15 receivedin an aperture 16 in the mica spacer 3. Insulator 15 is conveniently inthe form of a short ceramic tube or bushing, the lower end of whichrests on one of the anode fins 8. The presence of the wire 14 steadiesthe wire 10 in position during manufacture of the valve and facilitatesthe making of the connection between the wire 10 and the cathodeconnection 12.

In the alternative construction shown in Fig. 3 wire 10 is secured as byspot welding, to the cathode tube at 11, as before, but the remote endof the wire 10 extends into the insulator 15 which is now arranged toengage the aperture 16 in the spacer 3. In this alternative constructionthe projection 9 on the cathode is held against the mica spacer 3 by thespringiness in the wire 10 combined with the reaction of the anode finagainst the insulator 15 in the aperture 16. Again, in this con,

struction, the wire connection 10 does not lie along the surface of thespacer 3 and thus elfects no diminution of the insulation value of thespacer as between the cathode and the anode.

What I claim is:

l. A thermionic valve having an envelope cgntaining a tubular t ode an nd sur undin ai ca o said anode having radially disposed radiating finsextending therefrom, a mica spacer engaging the ends of said fins andhavingan aperture within which said cathode is located, said cathodehaving a peripheral projection to engage said spacer, and means forretaining said spacer against said. projection comprising a conductorsecured to said cathode at a region spaced along said; cathode from a aieet qa 9 1 add a dus qrh n in abutting engagementwiththe face Qfisaid-spacer remote from id rpis tion 94 t e e he end o Said conductorbeing extended to form a lead to said cathode terminating externally, sitlrnve epe a e am ins located in an aperture in said spacer to engagean end of one of said fins, and a metal strap secured to an intermediatepart of said conductor between its connection to said cathode and saidenvelope, said strap frictionally engaging said ceramic bushing.

said cathode at a region spaced along said cathode from said projection,a ceramic bushing located in an aperture in said spacer and engaging anend of one of said fins the end of said conductor making frictionalengagement with said bushing and being so resiliently formed betweensaid cathode and said bushing as to cause the projection on said cathodeto abut against the face of said spacer remote from the connectionbetween said conductor and said cathode.

References Cited in the file of this patent UNITED STATES PATENTS RonciMar. 22, 1938 Van Tol Feb. 28, 1956

